Regensburg 2019 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: Wetting, Fluidics and Liquids at Interfaces and Surfaces (joint session CPP/DY)
CPP 20.6: Hauptvortrag
Dienstag, 2. April 2019, 10:45–11:15, H13
Dynamic surface tension of soft solids — Mathijs van Gorcum1, Bruno Andreotti2, Jacco Snoeijer1, and •Stefan Karpitschka3 — 1University of Twente, Enschede, Netherlands — 2Université Paris-Diderot, Paris, France — 3MPI-DS, Göttingen, Germany
The contact line of a liquid drop on top of a solid surface exerts a nanometrically sharp surface traction, providing an unprecedented tool to study highly localized and dynamic deformations of soft polymer networks. The morphology is determined not only by bulk viscoelasticity, but also by solid surface tension. The latter may depend on strain, known as the Shuttleworth effect. Its impact on soft wetting is controversially discussed in recent literature. One of the outstanding problems in this context is the stick-slip instability of a moving contact line, which is observed above a critical velocity. Timeresolved measurements of the solid deformation are challenging, and the mechanism of dynamical depinning has remained elusive. Here we present direct visualizations of dynamic wetting ridges. Unexpectedly, the opening angle of the wetting ridge increases with speed, which cannot be attributed to bulk rheology. Instead, this effect points to an increase of solid surface tension not only in response to strain, but also depending on the rate of strain. Under this assumption, a criterion for depinning can be derived which is confirmed experimentally. We conclude that the surface tension of a solid is a truly dynamical quantity, following from a surface rheology that is different from the bulk, similar to what is known from liquid interfaces with surfactants.